Vulnerability Discussion

Leaving the user list enabled is a security risk as it allows anyone with physical access to the system to enumerate known user accounts without authenticated access to the system.

Check

Verify that the operating system is configured to disable the login screen user list for graphical user interfaces.

Note: If the system does not have the GNOME Desktop installed, this requirement is Not Applicable.

Verify that the login screen user list for the GNOME Desktop is disabled with the following command:

$ sudo grep -is disable-user-list /etc/dconf/db/gdm.d/*

/etc/dconf/db/gdm.d/00-login-screen:disable-user-list=true

If the variable "disable-user-list" is not defined in a file under "/etc/dconf/db/gdm.d/", is not set to "true", is missing or commented out, this is a finding.

Fix

Configure the operating system to disable the login screen user list for graphical user interfaces.

Create or edit the gdm profile in "/etc/dconf/profile/" to contain the following lines:

$ sudo vi /etc/dconf/profile/gdm

user-db:user
system-db:gdm
file-db:/usr/share/gdm/greeter-dconf-defaults

Create or edit the gdm database for machine-wide settings in "/etc/dconf/db/gdm.d/" with the following lines:

$ sudo vi /etc/dconf/db/gdm.d/00-login-screen

[org/gnome/login-screen]
disable-user-list=true

Update the system databases by updating the dconf utility:

$ sudo dconf update

If the login screen user list persists after updating the system databases, you can restart the GNOME Desktop without rebooting the system:

$ sudo systemctl restart gdm